x86, tls, ldt: Stop checking lm in LDT_empty
32-bit programs don't have an lm bit in their ABI, so they can't
reliably cause LDT_empty to return true without resorting to memset.
They shouldn't need to do this.
This should fix a longstanding, if minor, issue in all 64-bit kernels
as well as a potential regression in the TLS hardening code.
Fixes: 41bdc78544b8 x86/tls: Validate TLS entries to protect espfix
Cc: stable@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: torvalds@linux-foundation.org
Link: http://lkml.kernel.org/r/72a059de55e86ad5e2935c80aa91880ddf19d07c.1421954363.git.luto@amacapital.net
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
diff --git a/arch/x86/include/asm/desc.h b/arch/x86/include/asm/desc.h
index 50d033a..fc237fd 100644
--- a/arch/x86/include/asm/desc.h
+++ b/arch/x86/include/asm/desc.h
@@ -251,7 +251,8 @@
gdt[GDT_ENTRY_TLS_MIN + i] = t->tls_array[i];
}
-#define _LDT_empty(info) \
+/* This intentionally ignores lm, since 32-bit apps don't have that field. */
+#define LDT_empty(info) \
((info)->base_addr == 0 && \
(info)->limit == 0 && \
(info)->contents == 0 && \
@@ -261,12 +262,6 @@
(info)->seg_not_present == 1 && \
(info)->useable == 0)
-#ifdef CONFIG_X86_64
-#define LDT_empty(info) (_LDT_empty(info) && ((info)->lm == 0))
-#else
-#define LDT_empty(info) (_LDT_empty(info))
-#endif
-
static inline void clear_LDT(void)
{
set_ldt(NULL, 0);
